The orifice plate of a print head in an ink jet printer tends to collect debris such as paper dust during the printing process. The debris adheres to the orifice plate due to the occasional accumulation of ink droplets or an electrostatic charge. If left dirty, the accretion of debris and ink may impair printing quality by blocking or deflecting the passage of ink droplets during printing.
Some existing printers remove such debris with wipers that function as squeegees. A typical wiper has a cantilevered elastomeric blade extending perpendicularly to the orifice plate. As the plate slides past the blade, the blade is deflected to contact the plate with a force based on the modulus of the wiper material and the amount of the deflection. Because orifice plates on ink jet printers may have contours for functional reasons, the blade must be sufficiently flexible to variably conform to the surface it wipes, including reaching into slight recesses on the plate. Thus, an elastomeric material with good flexibility is needed.
Because a pen wiper should last the lifetime of the printer to avoid unwanted repairs, premature wear is a significant concern, particularly with the softer elastomers that are optimized for flexibility. Abrasion of the wiper over time is particularly a concern because a sharp, smooth wiper edge wipes best, resulting in a relatively high pressure on the small region of contact. Thus, a sharp edge may dull prematurely, resulting in impaired wiping.
To avoid the tradeoff between flexibility and wear resistance in other applications, elastomers have been reinforced by embedding harder particles in a rubber matrix. Typical filler particles are clay, calcium carbonate, carbon black, milled glass, glass fibers, and silica. The filler particles interact with the rubber matrix through mechanical attachments. In certain applications, the properties of elastomer have been enhanced by the use of silane coupling agents such as .gamma.-aminopropyltriethoxysilane and vinyltriethoxysilane, whereby a chamical bond was formed between the filler particles and the rubber matrix. Silica and glass particles have proven particularly effective, as they have appropriate surface chemistries available for bonding to the silane coupling agent.
However, bonded fillers are believed not to have been previously applied to printer applications, as the materials suitable for bonding may be prone to excessively wear the print head surface being wiped due to their abrasive nature. Furthermore, such particles increase friction in a circumstance in which reduced friction is preferred.
Therefore, there remains a need for an ink jet print head wiping apparatus having a wiper blade comprising a flexible elastomeric matrix containing particles of a harder material than the matrix, such that the particles resist wear to prolong the useful life of the wiper, the particle material may be a non abrasive but hard polymer such as polyethylene, which may be bonded to the matrix with a coupling agent such as silane.